Status: iShowU Studio 2, builds 2.3.1 and later, are natively compiled for the new Mac M1.
Capture performance is awesome. I couldn't perceive any system impact while capturing full screen @ 3840x1600. Great!
Encoding (composition) performance exceeds that of an an 2020 Intel iMac with AMD 5700.
Q: Is the app compatible with the new mac M1?
Yes. Studio2, as of build 2.3.1 and later is built for the M1.
Q: How fast is it?
Performance exceeds that of an 2020 Intel iMac with AMD 5700 (my other development machine).
In testing; I had the app running up to 120fps internally. That's 120fps while compositing & encoding. All using 6MP frames. If I were capturing something smaller; theoretical performance would be much higher.